About Cypripedium arietinum R.Br.
Cypripedium arietinum R.Br., the ram's head lady's slipper, is a small herbaceous perennial orchid that grows 10–40 cm (4–16 in) tall. It usually has 3 leaves, though it can sometimes have 4 to 5. A flowering stem normally produces just one flower, but the biflorum form may bear two flowers per stem. The flower is purplish-red with light veining, and its lip is white. It has three petals, one of which is modified into a densely hairy pouch marked with white and purplish tones. Its sepals are green with reddish-brown markings. Unlike other North American species of the Cypripedium genus, the side sepals of this species are free rather than fused; they are linear to linear-lanceolate in shape and somewhat spirally twisted. The remaining upper sepal is broadly elliptic to ovate-lanceolate. This species flowers in May and June, and has a diploid (2n) chromosome count of 20. Populations of Cypripedium arietinum are declining across most of eastern North America, but the species grows abundantly on Anticosti Island, which acts as a refuge for the plant. It is a forest understory species that occurs in coniferous to mixed forests, and in bogs dominated by Thuja occidentalis (northern white cedar), Larix laricina (tamarack), or Picea mariana (black spruce). In these habitats, it grows on small mounds formed by Sphagnum mosses. In Minnesota, it most often grows in upland coniferous forests dominated by Pinus resinosa (red pine) or Pinus banksiana (jack pine), in weakly acidic or nearly neutral soils that can be loam, clay, or sandy. In northern New England, it is commonly found in mixed hardwood and softwood forests.
